1. Field of the Invention
The present invention relates to a photopolymerizable composition which is improved in hindrance of curing caused by deactivation of radical by oxygen and which has excellent curability, and also to a process for formation of a resist pattern from the composition by exposing the composition to a visible laser.
2. Description of the Prior Art
To form a conductor circuit of, for example, printed wiring board, it has been conducted to coat a photosensitive resist on a substrate, subjecting the resulting resist film to light exposure and development to form a resist pattern, and subjecting the resist pattern to etching to remove the unnecessary portion of the substrate.
The above light exposure is conducted by, for example, light exposure via a photomask or direct drawing using a laser. The light exposure via a photomask has problems, for example, in that a considerable time is needed for the positioning of the photomask and that the positioning of the photomask is difficult when the resist has surface tackiness.
The direct drawing using a laser requires a highly sensitive resist because the time of laser application is very short. Therefore, so that the active radical generated in the resist by laser application is not deactivated by the oxygen in air and the resist can maintain the high sensitivity, it is generally conducted to cover the surface of the resist with an oxygen-shielding layer (e.g. a cover coating layer or a cover film layer).
The present inventors made a study with a view to developing a resist usable in the direct drawing using a visible laser, in which resist the active radical generated by laser application is hardly deactivated by the oxygen in air and consequently the sensitivity of the resist can be maintained. As a result, it was found out that the above object can be achieved by allowing a resist to contain a particular radical-protecting compound. The present invention has been completed based on the finding.